The present invention relates to an improved position determination system, and more particularly, to a position determination system that is resistant to interference caused by glint.
Certain types of position determination system, such as wheel alignment systems, use a vision imaging system that employs optical sensing devices to determine the positions of various target devices. A wheel alignment system of this type is capable of obtaining positional information about a vehicle, such as ride height, toe curve, tilt angle, and the angular relationship of the vehicle""s body relative to the vehicle""s wheels.
The wheels of a motor vehicle may be aligned in a number of ways. For example, an operator or an alignment technician can use a vision imaging system, such as a computer-aided, three-dimensional (3D) machine vision that employs image sensing devices, such as cameras, to determine the positions of various target devices. Although such vision imaging systems are typically used for alignment purposes, these systems can also be used to obtain other positional and angular orientation information about a motor vehicle. Examples of such apparatus and methods are disclosed in U.S. Pat. No. 5,724,743, entitled xe2x80x9cMethod and Apparatus for Determining the Alignment of Motor Vehicle Wheels,xe2x80x9d issued to Jackson, et al. on Mar. 10, 1998 and in U.S. Pat. No. 5,535,522, entitled xe2x80x9cMethod and Apparatus for Determining the Alignment of Motor Vehicle Wheels,xe2x80x9d issued to Jackson, et al. on Jul. 16, 1996, each incorporated herein by reference.
A computer is often used in conjunction with such vision imaging systems to calculate the orientation of the target device by identifying certain geometric characteristics on the target device. The computer takes perspective measurements and compares these measurements with the true image previously pre-programmed into the memory of the computer.
An example of a typical target device that can be used in a wheel alignment system is illustrated in FIG. 1. Target device 54 consists of a flat plate with a pattern of two or more differently sized circles 62, 63 marked in a pre-determined format thereon. Although a specific pattern is shown, a large number of different patterns can be used on the target device 54. In practice, a mathematical representation, or data corresponding to a true image (i.e. an image taken by viewing the target device perpendicularly to its primary plane) and the dimensions of the target device are preprogrammed into the memory of a computer so that, during the alignment process, the computer has a reference image to which the viewed perspective images of the target devices can be compared.
The computer calculates the orientation of the target device 54 by identifying certain geometric characteristics on the target device. The computer takes perspective measurements and compares these measurements with the true image previously pre-programmed into the memory of the computer.
The computer could, for example, calculate the center of each of the circles 62a, 62b by means of centroiding. This is a method commonly used by image analysis computers to determine the positioning of the center point or centerline of an object. Once the center points of the two circles 62a, 62b have been determined, the distance between the two can be measured. This process is then repeated for other circles in the pattern on the target device 54. These distances can then be compared to the true distances (i.e. non-perspective distances) between the respective centers. Similarly, the angle to the horizontal (or vertical) of the line joining the two centers can be determined. A calculation can then be made as to what the orientation of the target device 54 is.
Other methods of calculation can be used to determine the orientation of the target device 54. For example, the camera could sight onto only one of the circles, for example the circle 63, and by using the perspective image thereof (the distorted ellipse), calculate the orientation of that circle and, therefore, the orientation of the target device 54 as more fully described in U.S. Pat. Nos. 5,535,522 and 5,724,743.
Position determination systems using target devices and image sensing devices sometimes encounter problems when operated under strong light sources, such as the Sun. With the existence of strong light, the surface of the target devices may reflect the light in a direction entering the lens of the camera. The reflection of strong light into the camera produces a large white spot, called blooming. Blooming will interfere the receipt of images from the target devices. Although some of the target devices are made from materials that are 99% nonreflective of light, the 1% reflection of light from a strong light source, such as the sun, can still cause problem to the measurements until the sun moves off-target. Moving the target or optics as the Sun moves across the sky is impractical.
Accordingly, there exists a need for reducing the effects caused by glint to a position determination system. There is also a need to allow position determination in the presence of strong light sources. There is another need to provide a position determination system that is resistant to interference caused by glint and does not require movement or adjustment of equipment.
These and other needs are addressed by the present invention. The present invention provides an improved position determination system using target devices that prevent interference from strong light sources. This invention increases accuracy of measurements by eliminating interference from glint.
One aspect of the present invention relates to a target device for attaching to an object. The target device comprises a base configured for attaching on the object, a first target surface connected to the base, and a second target surface connected to the base, wherein the first target surface and the second target surface are on different planes. The planes on which the target surfaces locate are not parallel to each other. Since the target surfaces are on non-parallel planes, any light source producing glint on the first target surface will not cause glint on the second target surface. If light reflected by the first target surface causes interference, the image of the second target surface is still available for processing. Therefore, the interference caused by glint is eliminated.
According to one embodiment, a position determination system for measuring positional parameters of an object comprises: a target device which includes a base configured for attaching to the object, a first target surface connected to the base; and a second target surface connected to the base; wherein the planes on which the first target surface and the second target surface locate are not parallel. The position determination system has an image sensing device configured for forming a viewing path intersecting the target device and generating image information indicative of the geometric characteristics of the target device, and a data processing device configured to couple to the image sensing device for determining the orientation of the target device or the object on which the target device is attached based on the image information.
During measurement, the target device is attached to the object, such as a wheel of a vehicle, for marking each measurement. The images of the target surfaces are captured by the image sensing device, such as a camera, and analyzed by a data processing device, such as a controller or a computer coupled to the image sensing device.
According to one aspect of the present invention, the data processing device is configured for executing position determination software, such as alignment, and receiving image information representative of images captured by the image sensing device. The orientation of the target device used during the position determination process is determined based on the image information. The image information may be compared with reference information representative of images of the target device captured at a reference position. Alternatively, the reference position may be viewed from an angle perpendicular to the surface of the base. The reference information may be obtained from a hard drive memory.
As an example, the images of both target surfaces are captured by the image sensing device and transformed into image information to be processed by the data processing device. Whenever one of the target surfaces produces glint that interferes with the images received by the image sensing device, the other target surface, as discussed above, still provides reliable image information indicative of the geometric characteristics of that target surface. Therefore, interference from glint is eliminated.
Still other advantages of the present invention will become readily apparent from the following detailed description, simply by way of illustration of the invention and not limitation. As will be realized, the invention is capable of other and different embodiments and its several details are capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the drawing and description are to be regarded as illustrative in nature, and not as restrictive.